saint golden conference accolades conference … · design aws d1.1 - method based en ... •...

.

.

SCHOOL OF CHEMICAL AND METALLURGICAL ENGINEERING

SAINT Golden conference Accolades Conference centre

7-8 February 2018

New materials introduce different NDT challenges relating to health and life extension projects

Tony Paterson

University of the Witwatersrand

http://www.eie.wits.ac.za/

.

.


The bronze and iron ages show abilities in both casting and forging Use of heat and mechanical work

Where we came from


.

.


Iron Bridge 1779 Cast iron structure in compression following timber construction design methods


.

.


Industrial revolution Steam driven pumps Steam engines Steam boats Joining by forging and riveting


.

.


Sydney bridge

joined using

rivets


.

.


Electrical generators developed in the 1880’s

Arc welding followed in the late 1890s and early 1900’s

Shielded electrodes developed in 1910’s

MIG and TIG developed in the 1950’s

Hot rolled steel flats and sections dependent on composition only for strength used for

structures

[Research well aware of property effects of composition plus mechanical or thermal tempering

(EN (emergency number) UK nomenclature)]

Mathematical models for structural engineering developed in late 1940’s. The hypothesis of

homogenous isotropic material is still used as the base for the finite element programmes used.

A major market, the motor industry gradually adopted wrought steels from the 30’s and 40’s



.

FUSION WELDING as a means of joining

• Welding is an enabling technology that yields permanent joints.

• A small number of standard flat and shaped sections can be formed and joined to serve a

multitude of end user requirements.

• As forces can be aligned, thinner sections can be used.

• Stronger modern materials are more reliably manufactured. Consequently lighter

structures are designed. Welds have become more highly stressed. Concerns

previously masked by scale have emerged.

• Welding was initially anticipated only to meet structural imperatives.

• The 21st C has introduced other demands from welded fabrication.


.

.



9

Homogenous

Material assumed

Assessment of the discrete-continuous material interface between disciplines

The time space relationship between

physics, metallurgy and structural engineers



10

The relationship between structural engineers and

physical metallurgists

Silo training and interpretation

Homogenous

Material assumed

Heterogenous

Material assumed

Assessment of the discrete-continuous material interface between disciplines



.

.


The product platform

(1) Product/Structure, use,

and timing as defined

(4) Fabrication technologies,

suited, available, cost effective

(3) Material properties,

forms, availability

(2) Design

Modeling,

measurement,

detail

Final Product, real

operating circumstances

Client assurance is the NDT intent


.

.


the design decision process

Current and future perceived operational

circumstances


.

.


Structural design

Homogenous isotropic structural model assumes no change of structural strength or

toughness (ductility) of the weld.

Most often filler (nugget strength chosen is well above base material

e.g. 70xx electrodes (490MPa))

However as we move from hot rolled steels which rely on composition only to the

newer steels that combine composition and post composition thermal or mechanical

tempering the question arises as to whether this still holds.



1333oF/723oC

(CE*)

Carbon Equivalent * (Structural Steel) Strength increases with increasing CE

Grade Categories 0,0% < CE<0,30% 0,3% < CE <0,6% 0,6% < CE < 1,0%

Weldability of steels - composition

*Carbon equivalent example

CE = % Carbon + %Mn/6 + %Ni/15

. + % Cr/5 + %Cu/13 + % Mo/4 steels

Good weldability

Poor weldability

Ease of welding Excellent weldability


Introduction We will cover some theory and some practice that affects welding in general and steel and aluminium in particular. Theory 1. There is confusion between the von Mises stresses preferred by metallurgists and the

orthogonal stresses preferred by by structural engineers. They are directly related. 2. Most design is approached from a stress point of view. As stress = Young’s Modulus x (elastic) strain one can equally well use strain (deflection) as the base criteria Practice 3) Aluminium alloys show one third the Young’s modulus of steels and a ductility of around

one quarter that of mild steels

Three classes of dynamic loading leading to fatigue failure exist:

Fatigue

(3) Fatigue in cracked componentsCracks pre-exist, propagation controlled

fracture. Examples: almost any large

structures particularly those containing

welds: bridges, ships, truck

bodies/trailers, pressure vessels

Fatigue in uncracked componentsNo cracks preexist, initiation controlled

fracture: Examples are almost any small

components like gudgeon pins, ball races,

Gear teeth, axles crank shafts

(2) High Cycle (low strain) fatigueFatigue at stresses below proof stress

>10^4 cycles to fracture. Examples:

all rotating or vibrating systems like

wheels, axles engine components.

(1) Low cycle (high strain) fatigueFatigue at stresses above proof stress

<10^4 cycles to fracture. Examples: any

component subject to occasional overload,

core components of nuclear reactors, air

frames, turbine components.

.

15 SCHOOL OF CHEMICAL AND METALLURGICAL ENGINEERING


.

.


Consequence of failure

Low High

Structural considerations

Number of repeats and consequence of failure

Number of Low

Repeats

High

Simple, standard

mathematical

model

approaches

More attention to load effects.

Quality assurance checks on

fabrication and joints NDT

Detailed design to

production

methods NDT

Most sophisticated with high

level of detail plus laboratory

tests and prototyping NDT

E.g. welded safety sensitive

applications


.

.


Standards

Nomenclature SAE/AISI- steel grade nomenclature composition based

EN (1) - steel grade nomenclature composition based

EN (2) - performance (yield) based

Design AWS D1.1 - Method based

EN - performance based

As the standards philosophy is different, combining standards is not recommended

There is a complexity when standards interface as approaches are different


What has changed in steel mechanical properties over the last 20 years?

The motor industry has always been a very significant steel market By the late

1980s Californian environmental legislation was forcing change on the motor industry

by placing a premium on fuel efficiency, placing a premium on vehicle mass. This

led to a motor industry move towards aluminium (five fold increase per vehicle since

1975 to present). The steel industry responded by developing new, stronger, steels.

Steels are strengthened through two means, composition and tempering, the latter

including mechanical breakdown of grains and thermal treatment.

From a structural engineering point of view, new stronger steels were introduced.

These included the commonly used S235, S275 and S355 grades, the S designating

steel, the numbers minimum yield strengths. As the composition of all grades are

near identical, it is clear that tempering determines the difference in performance.

The question we seek to assess is the impact of welding on the materials



The limits of chemical composition as a guide to structural performance in

common structural steels has limits. Metallurgical and Mechanical treatment

is used to modify microstructure by reducing grain size (not cold rolling).

Note alloy overlaps compared to yield strength. There is a need to design to reduce

on site welding whether in an on site workshop or not because of the impact of

welding on increased mechanical treatment used for the higher grade steels.

Grade C% Mn% P% S% Si% CEE

S235 0.22

max

1.60

max

0.05

max

0.05

max

0.05

max

0.49

S275 0.25

max

1.60

max

0.04

max

0.05

max

0.05

max

0.52

S355 0.23

max

1.60

max

0.05

max

0.05

max

0.05

max

0.50

CE = % Carbon + %Mn/6 + %Ni/15 + % Cr/5 + %Cu/13 + % Mo/4)



.

.


For structural engineering steels

post weld heat treatment is not

required.

But what happens in the mushy

zone at temperatures above the

7230C transformation temperature.

Can we guarantee structural

performance assuming

homogenous isotropic properties?

Coarse fine


.

.


Creep As operating conditions change to higher temperature and pressures higher

performing creep resistant steels are required.

Creep resistant steels involve composition coupled to thermo-mechanical treatment.

But components such as vessels and pipes need to be joined. Post weld thermal treatment is required. What happens to the microstructure?

The Gleeble research tool allows precise

thermal control and can grow micostructure by

slowing the cooling time.



Effective and efficient welded connections.

The research tool – the Gleeble

• A Gleeble 3500 was installed a Wits in late 2014 and fully commissioned

by early 2015

• The Gleeble is a physical thermo-mechanical application device linked to

simulation programs. It is capable of reliably repeating a wide range of

experiments in a number of possible atmospheres.

• The Gleeble output compares real results with expected outcomes though

simulations and extends these simulations into other areas.

• This provides a data base of results to compare with single event physical

experiments.


Heating - direct resistance

- up to 10,000°C/second

- can hold steady-state

. equilibrium temperatures.

Cooling - High thermal conductivity

. grips

- quench air or water

- controlled cooling rates in

. excess of 10,000°C/second

. at the specimen surface.

Axial force - fully integrated hydraulic

servo system

- up to 10 tons static force

tension or compression.

Displacement rates up to 1000 mm/sec

Non-contact laser extensometry

provides feedback to insure accurate

execution and repeatability .

Thermo couple connections

The heart of the Gleeble





B) Simulation of the discrete-continuous material interface

of whole welded structures to facilitate design

Direct resistance heating provides rapid and precise temperature control – source DSI




B) Simulation of the discrete-continuous material interface

of whole welded structures to facilitate design

Water-cooled jaws plus quenching contribute to very fast cooling rates (source DSI)


Sealed chamber The sample is isolated from the

external atmosphere.

Vacuum – mechanical and diffusion pumps .

High vacuum down to 2E-5 Torr

Potential for - inert gasses

- active gasses

- varied relative humidity

- normal atmospheres

- normal and acid rain impacts

- industrial environments (SO2)

- marine environment (Cl)

The Thermo mechanical section of the Gleeble is

connected to simulation software through which:

• actual physical results can be compared with theory

• Results can be extended to develop stress strain

relationships suited to FEA’s

The heart of the Gleeble

The chamber



.

.


The 21st Century has introduced the challenges of:

• Globalisation

• The triple bottom line of planet, people, prosperity (e.g. International SHE)

• The finite limits of engineering material availability

• The finite limits of energy sources

• The finite limits of water

Globalisation has encouraged international standards generally drawn up from developed countries

lead.

From a systems control point of view input (method) specifications are preferred to output

(performance) specifications - But RSA has chosen the EN route.

Triple bottom line reporting places more emphasis on health. Internationally and locally health

legislation has been progressively tightened.

Based on standards, administration has become the driver rather than the facilitator. Check lists

supersede applied engineering skills; Inspectors have replaced supervisors.

Consequently, quality tends not to be built in but inspected out.


.

.


NDT DEMANDS FOR PROCESS PLANTS


.


• Process plants with an operational life of decades typically include (thin wall) pipes linking treatment

tanks, heat exchangers or distillation columns. Standard plates and pipes are formed, then

welded together into systems that meet prevailing or future perceived operating environments.

• Biofilm formation on inside surfaces encourages both bacteria growth and Microbial Induced

Corrosion (MIC).

• A particular group of process plants, pharmaceutical, dairy, food, beverage and brewing, are subject

to health legislation.

• International and local health legislation is increasingly demanding lower and lower bacterial (and

spore) counts (alive or dead) in the end product. Pasteurisation is no longer acceptable.

• Hygienic fabrication and operation are required to guarantee pharmaceutical and food safety.

• For hygienic fabrication, whilst good design standards exist, major gaps are found in the lack of

practical guidelines, education and, pertinent to South Africa, skill training and development together

with appropriate supervision

• Maintenance of existing plants decades old needs to comply with current health legislation

Note: In terms of health legislation sterilize, disinfect, sanitize, and clean represent

decreasing ranks.

Health related process plants


.


• Hygiene requirements, potentially more demanding to achieve than structural

integrity, are an addition to engineering fabrication/operational requirements.

• Welding is a source of surface roughness

• Welded area a very small part total area of installation

• Good design standards exist for hygienic fabrication

• Major gaps are found in the lack of practical guidelines

• Realistically, hygienic welded fabrication, particularly with on-site welding, is more

challenging, more costly.

• Heat exchanger tubes are faced with similar problems but related to MIC

• The NDT question is whether we are looking deeply enough into

non structural performance issues such as health and corrosion

Effective and efficient welded connections


• Depth δ increases with increased surface roughness, increased temperatures, and lower flow speeds

.

(Biofilm formation- not limited to health related sectors)

Source: A review of current and emergent biofilm control strategies

Manuel Simoes, Lucia C. Simoes, Maria J. Vieira

LWT - Food Science and Technology 43 (2010) 573–583)

δ




.



Scanning electron micrograph of a biofilm on the inner surface of a dispensing line.

Source Erna Storgårds Process hygiene control in beer production and dispensing VVT publication 410 2000

Yeast cells

Bacteria

Note protruding

fimbrae



Fe(OH)2

TUBERCLE

e Typical

Bottle shaped pit

Cl -

Cl -

Cl -

Cl -

Cl -

Cl -

Cl - Cl -

Cl -

e- e- e-

2H2O+O2 + 4e 4OH-

Large Surrounding cathode

Small anode

Fe 2+ Fe 2+ FeCl3

Fe 3+

2Fe(OH)2

Microbial Induced Corrosion – tubercle and pit Welding is particularly prone to MIC as welds include micro cracks


Biofilm build up on product contact surfaces- MIC

Also affects heat exchanger tubes


.


Progressive Microbial impacts of imperfections

Based on source- Presentation Knuth Lorenzen, European Hygienic Engineering & Design Group, October 2007

3) Weld imperfection effects on health – product flow

. HAZ surface roughness promotes biofilm growth

Crack indicative

of range of

welding concerns

o Porosity

o Cracks

10μ


Cleaning and disinfection fluids

will only affect the biofilm on

the outside lip of the crack

Flow and flow rate of cleaning

and disinfection fluids

Limited effect of clean in Place (CIP) processes

Based on source- Presentation Knuth Lorenzen,

European Hygienic Engineering & Design Group, October 2007

CIP chemical

concentration,

time and

temperature effects;

1) Polish

2) Etch

3) Mill

Note Dilution over

distance



.

.


Pipe manufacturing and fabrication

Manufacturing - measurement deviations result from:

• Rolling operation – rolling tolerances relate to the difficulty of keeping the sheet either a precise

thickness or perfectly flat (In addition, rolls are not set flat but bulge slightly at the centre.)

• Sheet anneal or stretch

• Slitting operation – width differences resulting from setting or tool wear

• Pipe forming operation – alignment, gap, welding effects and spring back

• Possible effects on pipe ends from cutting to length operation

• Possible transport effects related to welding stress relief and packaging.

The net result is pipes and tubes are neither circular nor of even wall thickness.

In the case of thin wall pipes related to hygienic fabrication the impacts can be significant in terms of

increased CIP operations.

Manufacturing effects may be overcome by using pipe end forming methods

Also, the potential move from 316L Stainless steel towards stronger

Duplex grades, e.g. 2304, could lead to even thinner pipe walls.


.

.


Configuration Random

orientation

>80%

Overlap

Aligned

major axis

>80%

Overlap

Random

orientation

>80%

Overlap

Aligned

major axis

>80%

Overlap

Material and wall thickness 316L Current

thickness

316L Current

thickness

2304 Half

thickness

2304 Half

thickness

Pipe to pipe % % % %

s-s low tolerance M1 (1) 17 47 1 12

s-s high tolerance M2 (2) 100 100 79 82

s-s M1 to M2 (3) 33 39 4 6

Pipe to bend (elbow)

s-b low tolerance M1 (4) 22 59 2 16

s-b high tolerance M2 (5) 58 85 6 26

Configuration Random

orientation

>80% Overlap

Aligned major

axis

>80% Overlap

Random

orientation

>80% Overlap

Aligned major

axis

>80% Overlap

Material and wall thickness 316L Current

thickness

316L Current

thickness

2304 Half

thickness

2304 Half

thickness

Pipe to pipe % % % %

s-s low tolerance M1 (1) 17 47 1 12

s-s high tolerance M2 (2) 100 100 79 82

s-s M1 to M2 (3) 33 39 4 6

Pipe to bend (elbow)

s-b low tolerance M1 (4) 22 59 2 16

s-b high tolerance M2 (5) 58 85 6 26


.

.


Strategy of sweating the assets - Life extension

This implies working existing assets either beyond design life or under different

operating conditions.

Older assets operated for decades are of older materials and older design

In Johannesburg one example is the practice of increasing water pressure

beyond design pressure to facilitate service delivery to an increasing population.

Clearly failures are to be expected – the weakest link will break first

What is the weakest link – when will it break – how can life be extended?

Currently one problem that is emerging is delamination on pressure and thermal

vessels and pipes. Others have been noted in welds.

Roll refurbishment that seeks to add wear resistant layers risks delamination if

not properly assessed

Whilst clients want to extend life, industrial research using NDT tools seems

appropriate.


.

.


One repair tool - Friction Hydro Pillar Process (FHPP):

FHPP was invented by The Welding Institute (TWI) in the early 1990’s

It is a solid state friction welding technique with inherent advantages over

conventional arc welding; i.e. reduced heat input, small HAZ, reduced

distortion, highly repeatable process

The technique involves axially rotating a consumable tool, under an applied

load, co-axially in a circular cavity, continuously generating and depositing

plasticized layers of material

A parallel sided hole-tool or a tapered hole-tool arrangement can be employed

Pinning or stitch welding can be achieved


.

.


Upset to be

removed

7mm min

Core for

possible

examination

7mm min support

Example of

application

with narrow

support


.

.


Initially constructed in 1844, modified in 1860 and later the Malahide Viaduct just north of Dublin, Ireland, was 176

m long, had 11 post-tensioned concrete beams spans mounted on 10 masonry piles supported on a stone weir.

The stone weir was required as the structure was susceptible to scour due to the tidal flow in the estuary. The

stone weir required regular maintenance. For more than150 years the weir structure had been susceptible to scour

and had a maintenance regime to control the risk. Stone discharges occurred in 1976 and 1996.

It was 6:22 pm on the 21st of August 2009 and a passenger train was crossing the Malahide Viaduct when the

driver noticed a portion of the viaduct beginning to collapse. The cause was found to be scour.

But, how could it be scour? What about the historic

knowledge of the scour risk and the maintenance regime?

Did they simply forget? The answer is ... yes.

As an organisation they forgot. This is called Corporate

Memory Loss.

Corporate Memory is “knowledge and information from the

company’s past which can be accessed and used for

present and future company activities” (Railway Accident

Investigation Unit, 2010).

When considering life extension Corporate Memory may

well be an issue worth investigating.

Look beyond the obvious.


.

.


What has all this to do with NDT?

Operating circumstances have changed – eg water sources

New NDT approaches and tools are required

On the health side more use can be made of borescopes linked by optical fibre

to a camera and/or PCT-

More important is the need increase levels of communication beyond simply

pass/ fail to assess what works from the point of view of assisting clients,

manufacturers and fabricators. Then an informed cost/benefit analysis can

be completed

On life extension projects, investigate beyond the obvious.

The FHPP process opens the opportunities to systematically examine

microstructure and to pin laminations to extend working life.


.

.


Conclusions

• The past 120 years have seen considerable changes in materials and joining methods

• Many existing structures are in excess of 40 – 50 years old and were designed differently

• The purpose of NDT is to provide client assurance that the structure will meet expectations

• This is different to ensuring that standards have been complied with.

• Materials have changed; standards have changed

• Health legislation has introduced a new challenge

• Operating circumstances have changed particularly regarding water

• Ultrasound can be used to kill bacteria

• Life extension of older plants introduced new challenges

• Consider the effects of corporate memory loss when considering life extension

• NDT approaches and techniques require continuous review and adaptation to changing

operating circumstances


.

.


SAINT Golden conference Accolades Conference centre

7-8 February 2018

New materials introduce different NDT challenges relating to health and life extension projects

Thank you Questions


saint golden conference accolades conference … · design aws d1.1 - method based en ... •...

Documents